Atmospheric Wind Flow

Question 1

What can be used to measure the wind direction and speed? How high above the ground are these placed?

Answer 1

• Wind vane to measure the direction
• Anemometer to measure the speed.
• 10m

Question 2

What is the Beaufort Wind Scale?

Answer 2

Scale for measuring wind speeds based on observation, not accurate measurement.

Question 3

Is Forecast wind direction measured in degrees True or Magnetic?

Answer 3

Degrees True

Question 4

Is ATC wind direction measured in degrees True or Magnetic?

Answer 4

Magnetic

Question 5

Below what altitude does friction start to affect the wind speed?

Answer 5

3000 ft

Question 6

What is Buys Ballot Law related to Thermal Wind?

Answer 6

With the cold air on your right, the tailwind increases with height.

Question 7

Does friction have more of an affect on the wind over land or over sea?

Answer 7

Over land.

Question 8

How much will wind over land deviate from isobars and what reduction in speed is typical?

Answer 8

• 45 degrees

- 70% geostrophic wind

Question 9

How much will wind over the sea deviate from isobars and what reduction in speed is typical?

Answer 9

• 10 degrees

- Almost no deviation in speed.

Question 10

What is a veering wind?

Answer 10

Clockwise change in direction

Question 11

What is a backing wind?

Answer 11

Anticlockwise change in direction

Question 12

What will occur in SH when wind gets closer to the ground?

Answer 12

It will slow down, reducing Coriolis force and veer the wind.

Question 13

What is a sea breeze?

Answer 13

Cooler air moving in over the land to replace warmer air that has risen.

Question 14

What is a land breeze?

Answer 14

Opposite flow of air to a sea breeze

• Usually less strong than a sea breeze
• Can hold a sea fog offshore until the sea breeze becomes strong enough to move it inland

Question 15

What are katabatic winds and when do they occur?

Answer 15

• Cooling air flowing down a mountain side.

- Occurs on clear, cloudless nights with lots of cooling.

Question 16

What factors affect the strength of the katabatic winds?

Answer 16

1. Length of the slope
2. Smoothness of the slope
3. Steepness of the slope
4. Length of the night

Question 17

What are anabatic winds?

Answer 17

Winds flowing up the mountain as the sun heats the mountain slopes by day and forces the warmer air to rise up the mountain.

Question 18

What is the Fohn Wind?

Answer 18

Larger temperature increase on lee side of mountain compared to wind side of mountain resulting in a hot dry wind on the lee side.

Question 19

What effects results from obstructions in the wind flow?

Answer 19

Mechanical turbulence causing rotors

Question 20

What are mountain and standing waves?

Answer 20

• Deflection of an airstream over a large mountain or mountain range.
• Standing wave is where the peaks and troughs of teh wave remain fixed in position.

Question 21

What are the requirements for mountain waves to form?

Answer 21

1. Wind flow at almost right tangles to the mountains
2. Wind strength near the mountain tops of at least 25 to 30 knots
3. Winds speed increasing with height
4. An upper stable layer sandwiched between an unstable layer at the surface.

Question 22

What is a gust defined as?

Answer 22

• A momentary increase in the speed of the wind above the mean reported speed.
• Only lasts for a few seconds
• Has to be greater than 10 KTS to be reported or forecast.

Question 23

What is a squall?

Answer 23

• A strong rise in wind speed which generally lasts for some minutes

Question 24

What is a gale?

Answer 24

Mean wind speed (measured over a period of 10 mins) is 34 kts or gusting to 43 kts.